/*
自己选择的路 ,跪着也要走完。朋友们 , 虽然这个世界日益浮躁起来,只
要能够为了当时纯粹的梦想和感动坚持努力下去 , 不管其它人怎么样,我
们也能够保持自己的本色走下去。
To the world , you will be a person , but to a person , you
will be the world .                               ——AKPower
*/
//作者:AKPower
//算法:
#include <iostream>
#include <cmath>
#include <algorithm>
#include <cstring>
#include <vector>
#include <map>
#include <queue>
#include <cstdio>
#include <string>
#include <stack>
#include <set>
#define IOS ios::sync_with_stdio(false), cin.tie(0)
using namespace std;
typedef long long ll;
const ll maxn = 1e6 + 10;
string s;
ll a[maxn];
int main()
{
    IOS;
    ll n;
    cin >> n;
    cin >> s;
    char las;
    ll id = 0;
    if (s[0] == '0')
        las = '1';
    else
        las = '0';
    for (ll i = 0; i < n;)
    {
        id++;
        while (i < n && las != s[i])
        {
            a[id]++;
            i++;
        }
        las = las == '0' ? '1' : '0';
        if (i == n)
            break;
    }
    ll ans = 0;
    a[id + 1] = a[id + 2] = 0;
    for (ll i = 1; i <= id; i++)
    {
        ans = max(ans, a[i] + a[i + 2]);
    }
    cout << ans << endl;
    getchar();
    getchar();
    return 0;
}
